/*
 * Copyright 2002-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.core;

import kotlin.reflect.KFunction;
import kotlin.reflect.KParameter;
import kotlin.reflect.jvm.ReflectJvmMapping;
import org.springframework.lang.Nullable;

import java.lang.reflect.Constructor;
import java.lang.reflect.Method;
import java.util.List;
import java.util.stream.Collectors;

/**
 * {@link ParameterNameDiscoverer} implementation which uses Kotlin's reflection facilities
 * for introspecting parameter names.
 * <p>
 * Compared to {@link StandardReflectionParameterNameDiscoverer}, it allows in addition to
 * determine interface parameter names without requiring Java 8 -parameters compiler flag.
 *
 * @author Sebastien Deleuze
 * @since 5.0
 */
public class KotlinReflectionParameterNameDiscoverer implements ParameterNameDiscoverer
{

    @Override
    @Nullable
    public String[] getParameterNames(Method method)
    {
        if (!KotlinDetector.isKotlinType(method.getDeclaringClass()))
        {
            return null;
        }

        try
        {
            KFunction<?> function = ReflectJvmMapping.getKotlinFunction(method);
            return (function != null ? getParameterNames(function.getParameters()) : null);
        }
        catch (UnsupportedOperationException ex)
        {
            return null;
        }
    }

    @Override
    @Nullable
    public String[] getParameterNames(Constructor<?> ctor)
    {
        if (ctor.getDeclaringClass().isEnum() || !KotlinDetector.isKotlinType(ctor.getDeclaringClass()))
        {
            return null;
        }

        try
        {
            KFunction<?> function = ReflectJvmMapping.getKotlinFunction(ctor);
            return (function != null ? getParameterNames(function.getParameters()) : null);
        }
        catch (UnsupportedOperationException ex)
        {
            return null;
        }
    }

    @Nullable
    private String[] getParameterNames(List<KParameter> parameters)
    {
        List<KParameter> filteredParameters = parameters.stream()
                // Extension receivers of extension methods must be included as they appear as normal method parameters in Java
                .filter(p -> KParameter.Kind.VALUE.equals(p.getKind()) || KParameter.Kind.EXTENSION_RECEIVER.equals(p.getKind())).collect(Collectors.toList());
        String[] parameterNames = new String[filteredParameters.size()];
        for (int i = 0; i < filteredParameters.size(); i++)
        {
            KParameter parameter = filteredParameters.get(i);
            // extension receivers are not explicitly named, but require a name for Java interoperability
            // $receiver is not a valid Kotlin identifier, but valid in Java, so it can be used here
            String name = KParameter.Kind.EXTENSION_RECEIVER.equals(parameter.getKind()) ? "$receiver" : parameter.getName();
            if (name == null)
            {
                return null;
            }
            parameterNames[i] = name;
        }
        return parameterNames;
    }

}
